Mexican government officials criticized the U.S. Border Patrol on Thursday for the fatal shooting of one of its citizens in a confrontation in Southern California this week, saying it opposed the use of lethal force in border control operations.

A U.S. border agent shot and killed a Mexican man on Tuesday while on patrol near San Diego, after being pelted with rocks while trying to apprehend a group of suspected illegal border crossers. One of the rocks hit him in the head.

“We firmly reiterate that the use of lethal force in border control operations is unacceptable,” Mexico’s foreign ministry said in a statement released by the Mexican consulate in San Diego.